Studies of the mechanisms responsible for the physiological and genetic derepression of asparagine synthetase in cultured hamster cells are continuing. Asparagine synthetase has been purified from beef pancreas and antibody has been prepared in rabbits. This antibody cross-reacts with the hamster cell enzyme. Immunological titrations and immunoprecipitation experiments will be performed to determine if elevated enzyme activity is associated with elevated levels of immunologically reactive protein and to measure the relative rates of enzyme synthesis and degradation in genetic variants and in wild type cells under various physiological conditions. If these experiments indicate that the increased levels of asparagine synthetase result from an increased rate of enzyme synthesis then cell-free translation systems will be utilized to quantitate mRNA levels. These studies will also be extended to asparaginase-sensitive and resistant leukemic cells and to revertants derived from the sensitive cells.